John Carmack of id Software warns that Doom 4 is likely to contain so much data that it may not fit on discs, not even Bluray.

In an interview at Quakecon, Carmack was asked whether the Rage PC demo on show was using the Super Texture pack that will be released in the future, and whether Doom 4 would utilise these updated graphics. His answer was the following (Turkish translation):

The videos are just using the normal game data. There is a decent chance we will fill more data than the PS3 and Blu-Ray DVDs for we ship on Doom 4, but we will have to see how much trouble it is maintaining two complete builds of the data. I would love to let the PC stream over the net when needed an extra detail, but the server and bandwidth that would take a significant commitment that I'm not sure we can make.
If this is the case, we may have to wait for Doom 4 on the next-gen of consoles as they will presumably use discs with a much bigger storage.

As a side note, Carmack also shows a willing to make a Rage 2 in the same interview. For now, Rage will be released October 4th, and for those PC players after those sexy textures, expect the Super Texture Pack sometime afterwards.